Tandy CM-4 User Manual

IMPORTANT
SERVICE
SAFETY PRECAUTIONS
Service
work should
be
performed
only
by
qualified
service technicians
who
are
thoroughly
familiar
with
all
of
the
following safety checks and
servicing
guidelines:
WARNING
1. For
continued
safety,
do
not
attempt
to
modify
the
circuit.
2.
Disconnect the
AC
power
before servicing.
3. Semiconductor
heat
sinks are
potential
shock haz-
ards when
the
chassis
is operating.
SERVICING
THE
HIGH
VOLTAGE
SYSTEM
AND PICTURE TUBE
When
servicing the high
voltage
system,
remove
the
static
charge by connecting a
10k
ohm
resistor
in
series
with
an insulated
wire
(such
as
a test probe)
between the chassis
and the
anode
lead.
(The
AC
line
cord should
be disconnected from
the
AC
outlet.)
1. The picture
tube
in this
display
monitor
employs
in-
tegral implosion
protection.
2. Replace with a
tube
of
the same
type
number
for
continued
safety.
3.
Do
not
lift
the
picture
tube
by the
neck.
4. Handle
the
picture
tube
only
when
wearing
shatter-
proof goggles
and after
discharging
the
high vol-
tage
anode completely.
X-RADIATION
AND
HIGH
VOLTAGE
LIMITS
1.
Be
sure
all
service
personnel are
aware
of the
procedures
and
instructions
covering
X-radiation.
The only
potential
source
of X-ray
in
a
current
solid-
state
display
monitor
is the picture
tube.
However,
the picture tube
does
not
emit
measurable
X-ray
radiation
if the high
voltage
is as
specified
in the
"high-voltage
check"
instructions.
It
is only when high
voltage
is
excessive
that
X-
radiation
is capable of
penetrating
the
shell
of
the
picture
tube, including
the
lead in
glass
material.
The
important
precaution
is
to keep
the
high vol-
tage below
the
maximum
level
specified.
2. It
is essential
that servicemen
have
available
at all
times
an
accurate
high
voltage
meter. The
calibra-
tion
of
this meter
should
be
checked
periodically.
3.
High
voltage
should
always
be kept
at the
rated
value
—
no higher.
Operation
at
higher
voltages
may cause
a failure of
the picture
tube or
high vol-
tage
circuitry
and, also,
under
certain conditions,
may
produce radiation
in excess of
desirable
levels.
4. When the high
voltage
regulator
is
operating proper-
ly
there
is
no
possibility
of
an X-radiation
problem.
Every
time
a
color
chassis
is serviced, the
bright-
ness
should
be
tested
while
monitoring the
high vol-
tage
with
a
meter
to be
certain
that
the high
voltage
does
not
exceed
the specified
value and
that it is
regulating
correctly.
5.
Do
not
use
a
picture
tube other
than that
specified
or make unrecommended
circuit
modifications to
the high
voltage
circuitry.
6.
When
troubleshooting
and taking test measure-
ments on
a
display monitor
with
excessive high vol-
tage, avoid
being
unnecessarily
close
to the
display
monitor. Do
not
operate
the display
monitor longer
than
is necessary
to locate
the
cause
of
excessive
voltage.
BEFORE RETURNING
THE DISPLAY MONITOR
Fire and
Shock
Hazard
Before
returning
the display
monitor
to the
user,
per-
form the
following
safety checks:
1.
Inspect
all
lead dress
to make
certain that
the
leads
are
not
pinched
or that
hardware
is
not
lodged be-
tween the
chassis and
other metal
parts
in the dis-
play
monitor.
2. Inspect
all
protective
devices
such as nonmetallic
control
knobs,
insulating
materials,
cabinet backs,
adjustment
and
compartment
covers
or
shield,
iso-
lation
resistor-capacitor
networks,
mechanical in-
sulators,
etc.
3. To be sure
that
no
shock hazard
exists,
check for
leakage
current in
the following
manner:
•
Plug
the
AC
line
cord
directly
into an 120 volt
AC
outlet. (Do
not
use
an isolation
transformer
for
this
test.)
•
Using two
clip
leads, connect
a 1.5k ohm,
10 watt
resistor paralleled
by a 0.15/iF
capacitor
in
series
with all exposed
metal
cabinet
parts
and a
known
earth
ground,
such
as
electrical
conduit
or electri-
cal ground
connected
to
earth
ground.
•
Use
a
SSVM or
VOM
with
1000 ohms
per-volt
or
higher
sensitivity
to
measure the
AC
voltage drop
across
the resistor.
(See
Figure
1.)

Tandy CM-4 Specifications

General

Brand	Tandy
Model	CM-4
Category	Monitor
Language	English